1. Field of Invention
The invention relates to a lithographic apparatus and illumination uniformity correction system. The present invention generally relates to lithography and more particularly to correcting for illumination irregularities so as to produce a uniform beam in a cross scan direction during lithography of an integrated circuit.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g., comprising part of, one or several dies) on a substrate (e.g., a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction.
A lithographic apparatus typically includes an illumination system, which is arranged to condition radiation generated by a radiation source before the radiation is incident upon a patterning device. The illumination system may, for example, modify one or more properties of the radiation, such as polarization and/or illumination mode. The illumination system may include a uniformity correction system, which is arranged to correct or reduce non-uniformities, e.g., intensity non-uniformities, present in the radiation. The uniformity correction devices may employ actuated fingers which are inserted into an edge of a radiation beam to correct intensity variations. However, a width of a spatial period of intensity variation that can be corrected is dependent on a size of an actuating device used to move fingers of the uniformity correction system. Furthermore, in some instances, if a size or shape of the fingers used to correct irregularities of a radiation beam is modified, then the uniformity correction system may compromise or modify in an unwanted manner one or more properties of the radiation beam, such as a pupil formed by the radiation beam.
Lithography is widely recognized as a key process in manufacturing integrated circuits (ICs) as well as other devices and/or structures. A lithographic apparatus is a machine, used during lithography, which applies a desired pattern onto a substrate, such as onto a target portion of the substrate. During manufacture of ICs with a lithographic apparatus, a patterning device (which is alternatively referred to as a mask or a reticle) generates a circuit pattern to be formed on an individual layer in an IC. This pattern may be transferred onto the target portion (e.g., comprising part of, one, or several dies) on the substrate (e.g., a silicon substrate). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate. In general, a single substrate contains a network of adjacent target portions that are successively patterned. To reduce manufacturing cost of ICs, it is customary to expose multiple substrates of each IC. Likewise, it is also customary that the lithographic apparatus is in almost constant use. That is, in order to keep manufacturing cost of all types of ICs at a potential minimum, the idle time between substrate exposures is also minimized. As a result, the lithographic apparatus absorbs heat which causes expansion of the apparatus's components leading to drift, movement, and uniformity changes.
In order to ensure good imaging quality on the patterning device and the substrate, it is beneficial to minimize or eliminate illumination irregularities. One way that this is carried out is by inserting “fingers” into an illumination beam at appropriate places to even out illumination. Various electro-mechanical sub-systems arrangements are utilized or proposed to manipulate the fingers into the appropriate positions for beam scanning and to move those fingers out of the beam path when they are not needed.
The market demands that sub-systems for manipulating the positions of fingers reliably operate in the environment of a lithography device so that the lithographic apparatus can perform lithography processes as efficiently as possible to maximize manufacturing capacity and keep manufacturing costs per device and maintenance low.
The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.